Battle of Mangdang

The Battle of Mangdang occurred in 198 AD when the army of Cao Cao attacked and destroyed the army of the Black Mountain Bandits as they were attacking Yan Province on Lu Bu's orders.

Background
In 198 AD, Cao Cao and Liu Bei, having defeated the imperial pretender Yuan Shu, secretly conspired to dispose of their fickle ally Lu Bu, who was ruling over Xu Province from Xuzhou. Lu Bu felt secure in his alliance and did not suspect a betrayal until his strategist Chen Gong intercepted a letter from Liu Bei which showed that the two of them were preparing their armies for battle. Lu Bu, feeling betrayed, led his army to besiege Liu Bei's capital of Xiaopei as he enlisted the help of the Black Mountain Bandits in attacking Cao Cao's base of Yan Province. Liu Bei was chased out of Xiaopei, which fell to Lu Bu's forces, and he wandered alone until he came across Cao Cao's army, which had arrived to support him against Lu Bu. Upon hearing of the bandits' attack on Yan Province, Cao Cao sent Cao Ren with 3,000 troops to take Xiaopei as he dealt with the bandit threat.

Battle
Cao Cao and Liu Bei met a band of 30,000 Black Mountain Bandits at the Mangdang Hills near Xiao Pass (which was defended by Chen Gong's army), and the bandit leaders Sun Guan, Wu Dun, Yin Li, and Chang Xi rode out with their spears set. However, Cao Cao's bodyguard Xu Chu rode out and easily beat them back, chasing them right up to Xiao Pass.

With the bandits temporarily defeated, Cao Cao was able to focus on retaking Xu Province. Lu Bu left Chen Gui in charge of Xuzhou and set out with Chen Deng to save Xiaopei from Cao Ren's army. Chen Deng betrayed Lu Bu by ordering Chen Gong to retreat from Xiao Pass, claiming that Xuzhou was already lost and that he had to return to Xu Province. Lu Bu and Chen Gong's armies accidentally attacked each other in the darkness, weakening each other. With Chen Gong's force withdrawn from the pass, Cao Cao had his army assault the bandits again, easily driving them out of Xiao Pass and scattering them in all directions.

Aftermath
Lu Bu and Chen Gong's armies attempted to return to Xuzhou, but they found that Mi Zhu had led an uprising there and fired arrows as Lu Bu's troops. Lu Bu and his army then attempted to head to Xiaopei, but discovered that it had fallen to Cao Ren's army, and Lu Bu was forced to flee east, with Cao Cao's army in pursuit. Lu Bu and his army fled to the fortress of Xiapi, while Liu Bei and Cao Cao made a triumphal entry into Xuzhou. With Xuzhou and Xiaopei retaken, Cao Cao now drew up plans for the recapture of Xiapi.